The present invention relates to a high resolution optical system for inspection and observation of fine pattern defects, foreign particles and the like that is typically performed in manufacturing process of semiconductors and flat panel displays and also relates to a method and an apparatus for detecting defects by using such optical system.
As a prior art, Japanese Patent Laid-open No. Hei 8-327554 discloses a technique for improving contrast of an object by changing an impinging angle of illumination depending on optical characteristics of the object to be observed.
In the above prior art, the impinging (incident) angle of the illumination is changed and determined so that minute unevenness on a surface of the object becomes obvious by improving the contrast of the unevenness. In such method, an optical system for oblique illumination and oblique detection is utilized, wherein the optical system changes a viewing mode of the object from bright field illumination to dark field illumination continuously by changing the impinging angle of the oblique illumination. However, for example, in the dark field illumination mode, it may be difficult to detect certain defects such as residual thin films, if any. Further, when semiconductor devices are inspected, minute unevenness (grains) may be appeared on a surface of metal wiring created in a metallization process. Such grains are not fatal for the semiconductor devices and therefore should not be detected as defects, however in the above prior art, it has been difficult to distinguish such grains from other defects properly to perform more reliable defect detection.